1. Field of the Invention
The present invention relates to a rotation transmission device. In addition, the present invention also relates to an image forming apparatus, such as copiers, facsimiles, printers and complex machines having two or more of copying, printing and facsimiling functions, which uses a rotation transmission device.
2. Discussion of the Background
Recently, a need exists for a color image forming apparatus (such as copiers, printers, facsimiles and complex machines having two or more of copying, printing and facsimiling functions), which can produce high quality color images at a high speed. In attempting to fulfill the need, a tandem color image forming apparatus is provided, which has plural color image forming devices (such as black (K), magenta (M), cyan (C) and yellow (Y) color image forming devices) and in which plural color images formed by the color image forming devices are transferred to a receiving material borne on an endless image bearing member (transfer belt) optionally via an intermediate transfer medium to form a multiple or full color image on the receiving material. In this regard, it is preferable that each of the image forming devices is a process cartridge detachably attachable to the image forming apparatus because it becomes possible that when one of the image forming devices is damaged, only the image forming device is replaced with a new image forming device. In this case, a rotation transmission device including a joint for connecting a shaft of a rotation driving device with a shaft of a rotatable member is typically used for the image forming apparatus.
In such a color image forming apparatus as mentioned above, color toner images formed by the color image forming devices are sequentially transferred onto an intermediate transfer medium or a receiving material borne on a transfer belt, resulting in formation of a multiple or full color image. In this regard, when the color toner images are not transferred to proper positions of the receiving material or the intermediate transfer medium, the image quality of the resultant color image deteriorates, i.e., a color image with color misalignment in which color images are overlaid while misaligned is formed. For example, when an image (such as character images and solid images) is formed on a colored background, problems in that an edge portion of the image is formed on the colored background and a white portion is formed between the edges of the image and the colored background occur if the color misalignment problem is caused. When a character image is formed on a white background, the edge portion of the character image looks blurred. Thus, color misalignment deteriorates image qualities.
One of causes for such color misalignment is rotational fluctuation of rotating members (such as photoreceptor drums and transfer belts). Specifically, rotation of such rotating members fluctuates at the same cycle as the rotation cycle of the driving members (such as driving rollers) for driving the rotating members. For example, the main causes of the rotational fluctuation of a photoreceptor drum are transmission errors of the drive transmission device for the photoreceptor drum (such as eccentricity of gears, and cumulative pitch errors of gears); and transmission errors of a joint provided to connect the photoreceptor drum with the drive transmission device (such as inclination of the axis of the joint and eccentricity of the joint).
Next, the phase matching technique will be explained.
Color misalignment is caused as follows. For example, when a black color image and a magenta color image are overlaid (e.g., a magenta image is formed on a black color solid image), the resultant combined image has color misalignment if the amplitude and phase of the vibration component of rotational fluctuation of a rotating member (such as photoreceptor drums) used for forming the black color image are different from those of a rotating member used for forming the magenta color image. Specifically, the difference between the amplitudes of the rotational fluctuation causes positional misalignment of the black color image and the magenta color image, resulting in color misalignment. In attempting to solve the color misalignment problem, Japanese patent application publication No. (hereinafter referred to as JP-A) 09-146329 (corresponding to U.S. Pat. No. 5,881,346) proposes a technique such that pattern color images are formed on a transfer belt to detect positional misalignment of the color images, the phases of the vibration components of rotational fluctuations are determined on the basis of the detection results, and phase controlling is performed such that the phases of the vibration components of the rotating members for the color images are identical to each other to control the positional misalignment.
However, each of the drive transmission members used for forming different color images (such as K, M, C or Y color images) has individual error. Therefore, the amplitude of the vibration component of rotational fluctuation of a rotating member for forming images with a color is different from that of the corresponding rotating member for forming images with another color. In the image forming apparatus disclosed in JP-A 09-146329, each of the rotational phases of the rotating members for forming different color images is corrected so that the rotational phases are identical to each other. In this regard, if the amplitudes of rotational fluctuations of the rotating members for forming different color images are the same, occurrence of the color misalignment problem caused by positional misalignment of the different color images can be prevented by conforming the rotational phases. However, in reality the amplitudes are not the same. Therefore, even when the rotational phases are conformed, the difference between the amplitudes causes the color misalignment problem.
Next, the coupling technique will be explained.
In attempting to improve the rotation accuracy of a combination of plural rotating members and the positional accuracy thereof at the same time, various rotation transmission methods using a joint for transmitting rotation of a driving member provided in an image forming apparatus to a rotatable member of an image forming device set to the image forming apparatus have been proposed.
For example, JP-A 2004-94204 (corresponding to U.S. Pat. No. 6,968,144) discloses a rotation transmission device using an involute spline joint to improve the rotation accuracy. By using an involute spline joint, rotation fluctuation at the coupling can be decreased but rotation fluctuation of gears serving as a decelerator and the joint itself remains uncontrolled. Therefore, it is necessary for the technique to improve accuracy of the parts used therefor, resulting in increase of the costs thereof.
FIG. 1 is a schematic perspective view illustrating a background rotation transmission device. The background rotation transmission device includes a photoreceptor 1 having a shaft 2, a first joint 3 (i.e., a photoreceptor-side joint), a second joint 4 (i.e., a drive-side joint), a photoreceptor driving member 5, and a driving motor 6. The photoreceptor 1 is axially supported by the shaft 2. One end of the shaft 2 serves as the first joint 3. In such a rotation transmission device, the driving motor 6 (such as DC servo motors and stepping motors) inputs a driving force to the second joint 4 via the photoreceptor driving member 5. In this case, when the second joint 4 is engaged with the first joint 3, the photoreceptor 1 is rotated by the driving force.
In addition, JP-A 2000-276030 discloses a joint system for independently transmitting driving forces to a photoreceptor, a developing device, etc. This joint system uses a twisted triangle pole-form joint for transmitting a driving force to the photoreceptor. However, the joint system has a drawback in that rotation fluctuation of gears serving as a decelerator and the joint itself remains uncontrolled. Therefore, it is necessary for the system to improve accuracy of the parts, resulting in increase of the costs thereof.
Even when the rotation phase controlling proposed by JP-A 09-146329 is performed, the color misalignment caused by amplitude difference among the rotation members used for forming different color images remains. This color misalignment caused by the amplitude difference is a problem. In order to improve the image qualities by reducing the amplitude difference, it is necessary to improve the dimensional accuracies of the parts used for the rotation transmission device (joint) and/or to improve the calculation accuracy in rotation angular velocity controlling for the photoreceptors, but costs increase in any case.
Because of these reasons, a need exists for a rotation transmission device which can reduce the amount of color misalignment without using high-accuracy parts, i.e., without increasing costs.